Band offsets and stability of WSe 2 /RuCl 3 van der Waals charge-transfer contacts

The layered Mott insulator α-RuCl 3 induces degenerate hole-doping in two-dimensional semiconductors due to its large electron affinity, making it a promising charge-transfer material for establishing ohmic contacts in electronic devices. In order to assess the applicability and guide the design of devices incorporating RuCl 3 it is critical to determine the electronic structure and robustness of the band offsets that underpin the transport properties of semiconductors in contact with RuCl 3 . Here, we apply micro-focused angle-resolved photoemission spectroscopy to determine the electronic structure of single-layer WSe 2 contacted to RuCl 3 on hexagonal boron nitride substrates. We find that formation of a functioning WSe 2 /RuCl 3 contact leads to a valence band shift of (0.68 ± 0.05) eV towards the Fermi energy in WSe 2 . The charge transfer effect is challenging to observe as it depends sensitively on fabrication conditions such as solvent exposure, quality of interface encapsulation and heating of RuCl 3 , imposing strict requirements on device design to attain high-quality contacts.